Problem Solving

AAPL wrote:A car traveled 60 mph from Belnap to Lincoln and 50 mph from Lincoln to Belnap. If the whole trip was 660 miles, how long did the round trip take?

A. 6 hours
B. 11 hours
C. 12.1 hours
D. 13.2 hours
E. 24.2 hours

The OA is C.

Whole trip was 660 miles. Which means one-way trip was 330 miles.
Time taken from Belnap(B) to Lincoln(L) = 330 / 60 = 5.5 hours.
Time taken from L to B = 330 / 50 = 6.6 hours
Time spent on round trip = 6.6 + 5.5 = 12.1 hours. Option C.

Has anyone another strategic approach to solve this PS question? Regards!

That's a perfectly valid approach.
Here's one slight modification:

Once we know that the total time = 330/60 + 330/50, we might also see what happens when we find a common denominator BEFORE adding the parts.
So, total time = 330/60 + 330/50
= (5)330/300 + (6)(330)/300
= (11)(330)/300
= (11)(11)/10
= 121/10
= 12.1

Cheers,
Brent

Hi AAPL,

We're told that a car traveled 60 mph from Belnap to Lincoln and 50 mph from Lincoln to Belnap and that the whole trip was 660 miles. We're asked how long (in hours) the round trip took. The answers to this question are 'spread out' enough that you can actually do some 'rounding' to determine the range that the correct answer must be in.

Since the two speeds are 50 mph and 60 mph, we know that the average speed would be some speed between those two. IF the ENTIRE tripe was done at 60 miles per hour, then the trip would take:
660 miles = (60 mph)(X hours)
X = 660/60 = 11 hours

IF the ENTIRE tripe was done at 50 miles per hour, then the trip would take:
660 miles = (50 mph)(X hours)
X = 660/50 = 13.2 hours

The overall trip was NOT done at just one of those two speeds though, so 11 hours is TOO fast and 13.2 hours is TOO slow. The correct answer has to be some value in between... there's only one answer that 'fits.'

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

AAPL wrote:A car traveled 60 mph from Belnap to Lincoln and 50 mph from Lincoln to Belnap. If the whole trip was 660 miles, how long did the round trip take?

A. 6 hours
B. 11 hours
C. 12.1 hours
D. 13.2 hours
E. 24.2 hours

The time for the entire trip was:

330/60 + 330/50 = 33/6 + 33/5 = 11/2 + 33/5 = 55/10 + 66/10 = 121/10 = 12.1 hours

Answer: C